The long range goal is to study virus structure at high resolution, in order to describe mechanisms for viral entry and assembly and to provide a basis for vaccine and drug design. The proposal includes work on reoviruses and rotaviruses (both dsRNA viruses with related replication cycles) and on papillomaviruses. The rotaviruses are a major worldwide cause of childhood diarrhea. Certain papillomaviruses are strongly associated with human cervical cancer. (1) X-ray crystallographic studies of reovirus cores, "molecular machines" that modify and extrude mRNA, will be carried out at 3.3 A resolution. (2) The structure of the rotavirus "inner capsid particle" (ICP), homologous in many functions to the reovirus core, will also be determined crystallographically. Both the reovirus core and rotavirus ICP structures represent a significant level of molecular complexity (about 700 A diameter) and crystallographic challenge (over 1000 A unit cell dimensions). Strategies for collecting the diffraction data using synchrotron sources have been worked out; phase determination will use low-resolution structure from cryo-electron microscopy as starting points. (3) Expression and crystallization of the reovirus "penetration" protein, u1, and of the rotavirus attachment and penetration protein, VP4, will be undertaken, with high resolution crystal structures as the goal. The structures of these proteins will be analyzed in order to understand how non-enveloped viruses penetrate cell membranes. VP4 is also directly relevant to the development of rotavirus vaccines. (4) The structure of the human papilloma virus (HPV) L1 protein will be determined, using recombinant pentamers expressed in E. coli. This approach parallels work from the previous grant period on polyoma virus VP1, which HPV-L1 is likely to resemble. L1 is a major component of proposed recombinant HPV vaccines.